Generally, in this type of engine, the exhaust gas is discharged into the atmosphere through an exhaust line bearing a means for depolluting this exhaust gas before it is discharged into the atmosphere.
Advantageously, this depollution means is a catalyst through which this gas flows, and which is intended to remove some pollutants contained therein. The main function of the catalyst, more particularly a so-called “three-way” catalyst, is to oxidize the unburnt hydrocarbons (HC) and the carbon monoxide (CO), and to reduce the nitrogen oxides (NOx), which are the pollutants that are usually present in the exhaust gas.
It is common knowledge that this type of catalyst can only fill its role when it has reached a minimum temperature of operation start or initiation, referred to as light-off (of the order of 200° C.). This temperature level is essential to allow reaction between the catalytic elements borne by the catalyst and the pollutants contained in the exhaust gas. However, notably during the engine cold running period that follows start-up of this engine, the rise in temperature of the catalyst is not fast enough, which causes discharge of the unprocessed exhaust gas into the atmosphere. An increase in the temperature rise speed of this catalyst is consequently necessary to provide exhaust gas depollution and thus to meet the standards applied to motor vehicle engines that are increasingly severe. This problem also arises when the engine is warm with a warm catalyst (at operating temperature) and when this engine runs at low speeds and/or low torques, such as at idle speed. In such configurations, the exhaust gas discharged from the engine is at such a temperature (below 200° C.) that it cannot keep the catalyst temperature high enough for it to be efficient and on the contrary cools it down by flowing therethrough.
Many solutions have been provided to this problem in order to rapidly increase the catalyst temperature. These solutions essentially consist in increasing the exhaust gas temperature by either raising, for a short time, the fuel/air ratio of the fuel mixture present in the cylinders by creating an air deficit in the case of a diesel engine or, in the case of a gasoline engine, by injecting more fuel into the cylinders with delayed combustions and by injecting in parallel air into the exhaust line so as to create afterburning of the exhaust gas upstream from the catalyst.
The major drawback of such solutions is to raise very significantly the fuel consumption and to be detrimental to the driving comfort. Furthermore, the fuel/air ratio increase or the exhaust gas afterburning causes an increase in the discharge of pollutants that will not be treated by the catalyst.
The present invention aims to overcome the aforementioned drawbacks by means of an engine intake control method that allows to rapidly raise the exhaust gas temperature while shortening the time required for initiation of the catalyst, and while minimizing the fuel overconsumption and reducing the discharge of pollutants that are produced and not treated during the catalyst temperature rise up to the light-off thereof.